For the caramel sauce: Combine brown sugar and water in a saute pan and stir over medium heat until sugar dissolves. Bring to a boil and cook until sugar turns a light, golden amber color. Remove from heat and whisk in butter. Add lemon juice and set aside.
Cut peel and pith off of oranges and slice into 1/8-inch thick rounds. Spray a spring form pan or 9” cake pan with cooking spray and line the bottom with parchment paper.
Pour caramel sauce in prepared pan and arrange orange slices atop the caramel.
In a medium bowl, combine dry ingredients for the cake, orange zest, cornmeal, flour, baking powder, and salt.
Place room temperature butter in the bowl of a stand mixer and add granulated sugar. Using the whisk attachment, cream together until light a fluffy.
Add eggs, one at a time waiting until the first is fully incorporated before add in the next. Follow with sour cream and vanilla.
Using a rubber spatula, gently fold in dry ingredients just until incorporated.
Pour batter over sliced oranges and caramel and place on a sheet tray in case the spring form pan leaks during baking.
Place sheet tray directly on the grill grate and bake 50-60 minutes or until a toothpick comes out clean when inserted into the middle.
Remove from the grill and let cool on the counter 10-15 minutes before unmolding.
Run a knife along the edges and remove spring form mold. Invert the cake onto a serving platter or cake stand and remove the bottom of the spring form pan.
Peel off parchment, slice and serve! Enjoy.
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